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Poll

Why does a guitar amp buzz stop when you're touching the strings?

Your body is grounding the guitar
- 14 (43.8%)
The guitar is grounding your body
- 5 (15.6%)
Touching the strings creates a ground loop
- 0 (0%)
The strings are acting like an antenna
- 9 (28.1%)
You've got an electric personality
- 4 (12.5%)

Total Members Voted: 32

Voting closed: September 26, 2013, 09:44:26 AM


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Author Topic: Guitar stops buzzing when I touch the strings  (Read 89204 times)

Scott Holtzman

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Re: Guitar stops buzzing when I touch the strings
« Reply #140 on: February 05, 2015, 03:37:41 AM »

Yes, an oldie but goodie thread comes back to life. I just had an interesting install gig that's on topic for this thread. I'm installing a new digital console with a digital snake in a church with a rather large platform/stage. It's some 60 ft wide and 3 ft tall. They're putting a portable stage directly in front of the main stage for their new Saturday night youth service. And this B-stage has a drum kit, electric guitar, electric bass, multiple acoustic guitars, and a bunch of singers. Just what you would expect for this sort of service. Last week I was there to assist with the first load-in and sound check for this new stage, and the e-guitar player was complaining about her guitar buzzing "again" and that it must be ungrounded because if she touches the metal pickup guard or holds the strings the buzzing will stop. This was a single-coil Telecaster which as we all know is subject to RF induced buzz. A quick demonstration of me moving the guitar close to her body (buzz) and moving it away (no buzz) showed that she was the source of the noise. Then I grounded myself on another back line amplifier I had previously tested for grounding, and had her touch my hand while her guitar was hanging on the strap in front of her and buzzing like crazy. As we could predict from this thread, the buzzing stopped.

OK, that's old news that we all understand, but here's the next experiment. I had her spin in a circle slowly in buzz mode while standing on the stage and the buzz didn't change. But when she stepped away from the stage and stood in front of it, the buzzing was reduced significantly. It was like the stage itself was radiating the same kind of buzz we get from neon signs in a bar.

A week later I was climbing around under the stage to hook up a few speaker drops and saw that it's all metal studding. And there's many J-boxes connected to the studs for strength. And lots of the receptacles are the orange isolated ground types. So I started to wonder if the metal studs under the wooden stage were grounded/bonded to the electrical system. Then today the tech director drops the big bombshell, that they regularly cross connect some of the dimmers to power stage boxes and non-dimming fluorescent fixtures, and just set the lighting console so that the "dimmer" channel can be only 0% or 100%. I explained to her that Triac dimmers never really get to 100%, it's more like 99% on, and that plugging audio gear into a Triac patched receptacle was a VERY bad idea that could be causing her buzz. Especially since she now tells me that ANY electric instruments she puts up on the stage, including digital drums, buzz like crazy.

My hypothesis is that the metal stage structure may never have been bonded to the electrical service ground, and there could be a bunch of DIY installed electrical receptacles that are improperly bonded to stage metal. That's might causing this stage to re-radiate the dimmer hash from the 99% full-on Triacs. Or something like that.

I'm supposed to be doing some stage box rewiring at this church in the next week or so, and should have time to set up an experiment with buzzing guitars and drums. I'll begin by bonding the metal stage structure to the ground in the service panel. I'll also bring an o-scope for the AC power and look for the tell-tale spike caused by a Triac dimmer at "full-on". If I'm correct, then bonding the stage superstructure to the service panel ground and un-patching the dimmer racks from the stage receptacles should eliminate the buzz in the e-guitars and d-drums. But we shall see.

Sounds like another really good reason that metal stages should be properly bonded to ground. In this case an ungrounded stage really COULD mess up the sound of the guitar with a bunch of extra buzzing.

Mike, in data centers and in transmitter shacks at radio stations we bond everything.  The fence, the racks, the conduit.  Usually a halo is installed for easy connection.  A giant ungrounded portable platform is an antenna, plain and simple.

For safety and RF reasons we should be as diligent in our grounding practices.  For portable it doesn't even have to be awesome, I would just get some welding cable (nice and soft, easy to role) and a selection of clamps.  For permanent structures Cadweld is your friend.

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Scott AKA "Skyking" Holtzman

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Jonathan Johnson

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Re: Guitar stops buzzing when I touch the strings
« Reply #141 on: February 05, 2015, 03:32:35 PM »

Sounds like another really good reason that metal stages should be properly bonded to ground. In this case an ungrounded stage really COULD mess up the sound of the guitar with a bunch of extra buzzing.

Previous discussions of stage grounding have centered around the human-safety aspect. This points out that there is also an electronics aspect. Where a metal-framed stage with a wood deck might be given a "pass" and not be grounded for the human-safety aspect since there is a nonconductive surface between the talent and the structure, your example shows that a wood-decked stage with a metal substructure should still be grounded for technical reasons if not for human safety.
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Stop confusing the issue with facts and logic!

Mike Sokol

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Re: Guitar stops buzzing when I touch the strings
« Reply #142 on: February 05, 2015, 04:32:36 PM »

Previous discussions of stage grounding have centered around the human-safety aspect. This points out that there is also an electronics aspect. Where a metal-framed stage with a wood deck might be given a "pass" and not be grounded for the human-safety aspect since there is a nonconductive surface between the talent and the structure, your example shows that a wood-decked stage with a metal substructure should still be grounded for technical reasons if not for human safety.

That's exactly my point. Currently whatever is happening around this stage or its AC power distro is making it nearly unusable for electrically amplified instruments with high-impedance signals. Hard-wired low-z mics seem to be fine. And RF mics seem to be fine. But anything hooked up with unbalanced connections is a buzz factory. So any single-coil pickup guitar is nasty, and a digital drum kit with unbalanced outputs run into multiple DI boxes is buzzy. At first blush it appears the tech crew is doing everything right. But the buzzing is making them do dangerous things, like cutting off ground pins on extension cords. Again, that's a recipe for disaster. I'm going to look at this stage very closely over the next few weeks and try a few grounding/bonding experiments while instruments are buzzing on stage. This could become the poster child for properly grounding/bonding metallic stage structures, even if they're NOT a shock hazard for the musicians.

Again, this is all speculation, but I could be on to something.... 
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Mike Sokol
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Mike Sokol

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Re: Guitar stops buzzing when I touch the strings
« Reply #143 on: February 05, 2015, 06:11:02 PM »

Previous discussions of stage grounding have centered around the human-safety aspect. This points out that there is also an electronics aspect.

This also suggests that something like an non-grounded metal railing around a stage could cause guitars to buzz a lot more than usual. What about drop-ceiling grid? I know that the drop ceiling grid in my kitchen isn't bonded to ground. Doesn't that become a big antenna for radiating buzz? Of course, I don't play a lot of guitar in my kitchen, but I've been in a lot of performance spaces with a metal grid drop ceiling.

Seems like a really interesting area of study, especially since it could help make stages safer in addition to being electrically quieter.
« Last Edit: February 05, 2015, 06:27:18 PM by Mike Sokol »
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Mike Sokol
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Stephen Swaffer

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Re: Guitar stops buzzing when I touch the strings
« Reply #144 on: February 05, 2015, 08:41:18 PM »

Most drop ceilings have lights installed in them. Can lights would effectively ground the grid, flourescent troffers might be iffy because of paint.  However, I have never met a drop ceiling grid that wasn't happy to provide an effective ground for the electrician on top of a fiberglass ladder.

The metal framing is a safety issue in that if a hot wire in one of the boxes touches the box it will energize the framing.  If this were properly wired (at least as inspected around here) the boxes would all be grounded regardless of the receptacle configuration.

Another typically ungrounded metal screen is the wire mesh used for stucco, etc.  Out of sight out of mind!  In older buildings, tin ceilings are usually ungrounded.  The one in our church auditorium was actually energized for some time due to some volunteer wiring.  Surprisingly, it never created a hum issue in the sound system.
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Steve Swaffer

Mike Sokol

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Re: Guitar stops buzzing when I touch the strings
« Reply #145 on: February 05, 2015, 09:14:25 PM »

Another typically ungrounded metal screen is the wire mesh used for stucco, etc.  Out of sight out of mind!  In older buildings, tin ceilings are usually ungrounded.  The one in our church auditorium was actually energized for some time due to some volunteer wiring.  Surprisingly, it never created a hum issue in the sound system.

Just a clarification. I'm not suggesting that an ungrounded structure like a metal ceiling will cause a HUM. My point is that it can cause a BUZZ. Those are two totally different sounds caused by different interferences. While HUM is typically caused by ground loop currents circulating in low-z signal shields connected between different pieces of audio gear, BUZZ can occur when high frequency energy caused by dimmers, switching power supplies and neon signs radiates through the air and couples into high impedance audio circuitry such as single coil guitar pickups.

The first thing I do when troubleshooting these noises is to determine if we're hearing Hum, Buzz, Hiss or Hash (which I've covered in another thread) then try to define just what the noise source is. For instance, I had an electric keyboard with a BIG 60-Hz HUM a few months ago which was NOT a ground loop. They had used a non shielded speaker cable to go from the keyboard output to the DI box input. Again, this didn't BUZZ, but it really HUMMED. I guess it Hummed rather than Buzzed because the keyboard had a low enough output impedance that it shunted out the high "buzz" harmonics, but allowed a magnetic coupling to the 60 Hz sine waves in the electrical wiring all around them. 
« Last Edit: February 06, 2015, 12:35:37 AM by Mike Sokol »
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Mike Sokol
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Stephen Swaffer

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Re: Guitar stops buzzing when I touch the strings
« Reply #146 on: February 05, 2015, 10:40:31 PM »

I'm not suggesting that an ungrounded structure like a metal ceiling will cause a HUM. 

Understood-and since it did not create an issue maybe it is not surprising-in this case I wondered why 2000  + sq feet of energized tin, in close proximity too speaker wiring and parallel to choir mic (condensers) snake wiring for 75 feet did not induce some hum.  Perhaps, since no current was flowing there would not have been any magnetic fields.

What I find interesting is the various wiring schemes over the years.  When our building was converted from gas lighting to electric in the 30's all of that wiring was done with rigid conduit.  Even though it is rusty in many places, it still provides a good ground electrically-not sure how good it is for technical gear as all of that is on newer wiring.  We did have a bad CFL create a lot of noise in the system-and they are run on the rigid conduit wiring.
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Steve Swaffer

ProSoundWeb Community

Re: Guitar stops buzzing when I touch the strings
« Reply #146 on: February 05, 2015, 10:40:31 PM »


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